Upload & Sell: On
I own both and agree with Jammy. If I were doing weddings now, I'd have a pair of d700s. The d300 is very good and certainly would work okay as a wedding/event camera, but the d700 is simply a better tool for that application.
But, that depends greatly on you, your style of shooting, with/without flash, very high ISO use? and lastly, the raw conversion program that you use and whether or not you manipulate the files heavily in post.
ISO 1600 on the d300 is good, but ISO 3200 on the d700 is slightly better. That said, if I get the exposures correct, I do very little processing with either body, unless I feel like juicing up a shot. I use Phase One's Capture One for conversion and CS4 for final edits.
Another thing is that I still use flash a great deal. I have 3 sb-800s that I like to set up off camera, when possible and I do a lot of bounce shooting with the flash on camera at higher ISOs, when I can't use off camera flash.